How it began
The dolos was invented in 1963 at the port of East London, South Africa, after a major storm that year damaged the breakwaters of the city's artificial harbor. The design is usually credited to Eric Merrifield, East London harbor engineer from 1961 to 1976. Aubrey Kruger, a harbor draftsman, later said that he made the first model at home over lunch from three pieces of broomstick nailed into an H with one leg turned through 90 degrees, and that Merrifield asked him to draw a plan. The first dolosse were laid on the East London breakwater in 1964.
How it works
A dolos is a block of normally unreinforced concrete poured in a steel mold, weighing up to 8 tonnes in the original form and up to 22 tonnes in later designs. Dolosse are placed on top of each other by crane and form an interlocking but porous and slightly flexible wall. They work by dissipating the energy of waves rather than blocking it, deflecting most of it to the side, which makes them harder to dislodge than objects of similar weight with a flat face. Over time the waves shift them so that they become more entangled.
How it spread
Because the design was not protected, it was adopted freely in other countries. Dolosse protect harbor walls, breakwaters and shore earthworks. In the United States they were used to reinforce the jetties at Humboldt Bay in California in the 1980s, as an artificial reef at Dania Beach in Florida, and in rivers of the Pacific Northwest to control erosion and restore salmon habitat.
Who pushed back
Credit for the invention is contested. Merrifield received the Shell Design Award and a gold medal from the Associated Scientific and Technical Societies of South Africa, while Kruger never formally received credit. Merrifield died in 1982 and Kruger in 2016. The design was never patented. Merrifield said he wanted it to benefit humanity, while Kruger said Merrifield had been advised that work done in office hours for the state railways and harbors administration could not be protected.
Where it stands today
Dolosse are still cast and placed in great numbers as a form of coastal protection. They remain in use on South African coasts, including at Cape Town and on Durban's South Pier, and on breakwaters abroad. The name comes from an Afrikaans word for the knucklebones used as playthings and in divination.
